The present invention relates to a tapping valve comprising a housing which can be connected to a pipe and a connection piece with a drill arranged therein for tapping the pipe.
Friedel, U.S. Pat. No. 5,345,964 (=EP 572,817) discloses a tapping valve including a housing which can be connected to a pipe, particularly by welding. The housing of the valve and the pipe are preferably made of a weldable plastic, particularly polyethylene. A saddle of the housing includes a heating coil for electric welding. The housing further comprises a connection piece in which a metal guide sleeve is integrated, particularly by injection molding. Along its outer surface, the guide sleeve has ribs, pins or the like to secure it rotationally and axially in the plastic material of the connection piece. The guide sleeve is provided with an internal thread for a drill whose external thread engages this internal thread. After the valve and the pipe have been joined together, the guide sleeve makes it possible to drill a hole into the pipe. Furthermore, a branch socket to connect a branch conduit is coupled to the connection piece. This valve makes it possible to tap a pipe under pressure, i.e., without having to block the medium flowing through the pipe, particularly water or gas. The normal pressure in water supply networks can be as high as 16 bar and in gas supply networks 10 bar.
Louthan et al., U.S. Pat. No. 4,258,742 discloses a plastic tapping valve, which does not include a guide sleeve for the drill. The drill is screwed directly into an internal thread of the connection piece. The internal thread is formed in the connection piece after production or injection molding of the plastic housing, and the drill is subsequently screwed into the internal thread, which extends over the entire length of the connection piece. Tapping of pipes under pressure is not readily possible with such a tapping valve, since after tapping, the flowing medium under pressure can inadvertently escape through the thread area between drill and connection piece due to manufacturing tolerances. If the specified tolerances are too tight, substantial torques will be required to carry out the tapping, so that there is a possibility of damage to the tapping valve or even the pipe.
Accordingly, it is an object of the invention to provide an improved tapping valve.
Another object of the invention is to provide a tapping valve which assures a high degree of functional reliability without adding a lot of structural complexity.
A further object of the invention is to provide a functionally reliable tapping valve which can be manufactured at low material and production cost.
An additional object of the invention is to provide an improved pressure tapping valve which enables pipes to be tapped under pressure without any problem.
It is also an object of the invention to provide a tapping valve which requires only a low torque to tap the pipe.
Yet another object of the invention is to provide a tapping valve which assures a high degree of functional reliability.
These and other objects are achieved in accordance with the present invention by providing a tapping valve comprising a housing which can be connected to a pipe, and a connection piece with a drill arranged therein for tapping the pipe, wherein the connection piece has an initially cylindrical inner surface, and the drill or a sleeve in which the drill can be moved axially by a threaded connection, has an external thread which engages the inner surface of the connection piece, and rotation of the drill or sleeve in a forward direction causes the external thread on the drill or sleeve to form an internal thread in the inner surface of the connection piece.
The tapping valve according to the invention is distinguished by its simple, functionally suitable structure. It permits tapping of a pipe with a high degree of functional reliability, including the tapping of pipes under pressure. The drill, or a sleeve that is provided to guide the drill, has a self-cutting thread, which during the tapping process directly cuts or presses into the otherwise cylindrical interior surface of the connection piece. The flanks of the thread are configured with an acute angle to facilitate penetration into the inner surface of the connection piece. The plastic thus displaced flows into the root of the thread where it provides a seal. The penetration depth of the flanks of the thread into the inner surface of the connection piece is selected so as to ensure an automatic seal against the medium under pressure underneath the drill.
At the front end of the thread, in the direction of forward movement, the external thread diameter is specified to be larger by a predetermined amount than the diameter along the rest of the thread. Thus, the front end of the thread causes an increased displacement of plastic, particularly polyethylene, compared to the rest of the thread area, which is significantly longer. This substantially reduces the torque required to screw the thread into the plastic since the long thread area with the smaller diameter, compared to the front thread area, easily passes through the thread that has previously been cut or pressed into the plastic of the inner surface of the connection piece by the larger diameter front thread area.
Compared to tapping valves that contain a prefabricated thread in the inner surface of the connection piece, manufacturing tolerances are practically insignificant, and a reliable seal is ensured between the external thread of the drill or the sleeve and the thread that is produced in the inner surface of the connection piece as the drill or sleeve is screwed in. When the drill or sleeve is reversed, its external thread automatically finds the previously created thread in the inner surface of the connection piece, so that the drill or sleeve can return to the desired end position while still being reliably sealed.
In one advantageous embodiment, the drill or the sleeve which receives the drill is directly integrated into the connection piece during production of the tapping valve. It is particularly preferred to integrate the drill or sleeve into the connection piece by injection molding. The inner surface of the connection piece into which the thread is later to be cut is cylindrical. Thus, the inner surface of the connection piece comprises an integrated thread area corresponding to the thread of the drill or the sleeve.
During tapping by the drill, or during rotation of the sleeve, the drill or sleeve is screwed out of the molded thread area of the connection piece, also referred to as a mandrel, into the cylindrical inner area of the connection piece. According to the invention, the driving thread is cut in this area. The displaced plastic material is compressed into the thread flanks and is formed into a thread. As the drill or sleeve is reversed, the thread flanks again cut into the precut thread profile in the inner surface of the connection piece and compress the plastic material in the flanks. This ensures a reliable seal even during reverse motion.
The thread geometry according to the invention prevents chip formation, which would normally result in a metric ISO or fine-pitch thread. It should be noted that in a tapping valve, chip formation during or after the tapping process or rotation of the sleeve is not acceptable, as it would contaminate the pipe network. Advantageously, in the forward movement direction, in front of the first thread area with the enlarged thread diameter, there is a thread inlet area in which the diameter of the xe2x80x9cthread toothxe2x80x9d increases continuously starting from the thread root diameter of the drill or sleeve, until the outside diameter of the first area is reached. Consequently, there is no cutting edge or the like, which would lead to an undesired chip-forming removal of plastic.
The thread inlet area extends over a predetermined circumferential angle, preferably at least 90xc2x0, and advantageously at least 180xc2x0. Advantageously, the thread inlet at maximum extends up to a circumferential angle of 360xc2x0, preferably up to 180xc2x0.
The thread is initially cut into the cylindrical inner surface of the connection piece or mandrel by means of the first thread area, and after being formed is compressed in the subsequent turns of the second thread area. According to the invention, the plastic thus displaced is compressed in the thread flanks and is formed as a thread in the inner surface of the connection piece. This achieves an economically efficient production of the tapping valve overall and ensures the sealing function as the drill or sleeve is moved while subjected to the pressure of the medium flowing through the tapped pipe after the pipe has been tapped.
Further aspects and preferred embodiments of the invention are described hereinafter.